Method for preparing compact fine-grain magnesium aluminate spinel ceramic through low-temperature sintering

Abstract

The invention discloses a method for preparing compact fine-grain magnesium aluminate spinel ceramic by low-temperature sintering, which comprises the following steps: S1, mixing ethanolamine, magnesium acetate tetrahydrate and water according to a certain proportion to obtain a mixed solution A; s2, mixing citric acid, aluminum isopropoxide and water according to a certain proportion to obtain a mixed solution B; s3, slowly adding the mixed solution A into the solution B in the step S2 to form uniform colloid; s4, drying the colloidal solution to obtain a dried precursor; s5, performing low-temperature calcination on the precursor to obtain nano magnesium aluminate spinel powder; s6, carrying out ball milling and spray granulation to obtain spherical granulation powder with uniform particle size; s7, performing dry pressing molding and cold isostatic pressing molding to obtain a to-be-sintered ceramic biscuit; and S8, sintering in a muffle furnace to obtain the final magnesium aluminate spinel ceramic. The powder is subjected to ball milling, spray granulation, dry pressing forming and cold isostatic pressing forming, and then the compact fine-grain magnesium aluminate spinel ceramic is prepared through low-temperature sintering.

Description

Technical Field

[0001] This invention belongs to the field of ceramic preparation technology, and in particular relates to a method for preparing dense fine-grained magnesium aluminum spinel ceramics by low-temperature sintering. Background Technology

[0002] Magnesium alumina spinel ceramics, due to their excellent mechanical properties and chemical stability, have wide applications in transparent armor, high-temperature windows, the semiconductor industry, and refractory materials. However, the practical application of magnesium alumina spinel ceramics still faces many challenges. For example, high-purity raw materials are expensive, sintering temperatures are typically above 1600℃, and a certain amount of sintering aids are usually required, resulting in low material purity that cannot meet the requirements of semiconductor applications. Furthermore, high-temperature sintering usually means grain coarsening; the grain size of magnesium alumina spinel ceramics is typically several micrometers or larger, thus affecting the material's mechanical properties. In addition, the addition of sintering aids makes it easier for second-phase impurities to form at grain boundaries, thereby reducing grain boundary strength. Therefore, we urgently need high-purity, highly sinterable magnesium alumina spinel powder to prepare high-purity, dense, fine-grained magnesium alumina spinel ceramics at low-temperature conditions. Summary of the Invention

[0003] The main technical problem solved by this invention is to provide a method for preparing dense, fine-grained magnesium aluminum spinel ceramics by low-temperature sintering. After the powder is ball-milled, spray-granulated, dry-pressed, and cold isostatically pressed, dense, fine-grained magnesium aluminum spinel ceramics are prepared by low-temperature sintering in an atmospheric pressure and air atmosphere.

[0004] To solve the above-mentioned technical problems, one technical solution adopted by the present invention is: a method for preparing dense fine-grained magnesium aluminum spinel ceramics by low-temperature sintering, comprising the following steps: S1: Mix ethanolamine, magnesium acetate tetrahydrate and water in a certain proportion to obtain mixed solution A; S2: Citric acid, aluminum isopropoxide, and water are mixed in a certain proportion to obtain mixed solution B; S3: Slowly add the mixed solution A obtained in step S1 to the solution B in step S2 to form a uniform colloid; S4: Dry the colloidal liquid obtained in step S3 to obtain a dried precursor; S5: The precursor obtained in step S4 is calcined at low temperature to obtain nano-magnesium aluminum spinel powder. S6: The magnesium aluminum spinel powder obtained in step S5 is ball-milled and spray-granulated to obtain spherical granulated powder with uniform particle size. S7: The magnesium aluminum spinel granulated powder obtained in step S6 is subjected to dry pressing and cold isostatic pressing to obtain a ceramic green body to be sintered. S8: Place the ceramic blank formed in step S7 onto an alumina sintering plate and sinter it in a muffle furnace to obtain the final magnesium aluminum spinel ceramic.

[0005] Furthermore, in step S1, the mass ratio of ethanolamine, magnesium acetate tetrahydrate, and water is 1:(1-20):(30-100). In step S2, the mass ratio of citric acid, aluminum isopropoxide, and water is 1:(10-60):(30-100). The mass ratio of ethanolamine in solution A to aluminum isopropoxide in solution B is 1:(10-60).

[0006] Furthermore, in step S1, the mixing reaction temperature is 30–100°C, and the reaction time is 1–60 h.

[0007] Furthermore, in step S2, the mixing reaction temperature is 30–100°C, and the reaction time is 1–60 h.

[0008] Furthermore, the reaction time in step S3 is 1 to 60 hours.

[0009] Furthermore, in step S4, the drying temperature is 30–100°C, and the drying time is 1–60 h.

[0010] Furthermore, in step S5, the calcination temperature is 700–1200℃, and the calcination time is 1–10 h.

[0011] Furthermore, in step S6, the ball milling method is planetary ball milling, the ball milling speed is 200-400 rpm, and the ball milling time is 10-30 h.

[0012] Furthermore, in step S7, the pressure for dry pressing is 10-50 MPa, the pressure for cold isostatic pressing is 200-300 MPa, and the pressure is held for 5 minutes.

[0013] Furthermore, in step S8, the sintering temperature is 1200–1400℃ and the sintering time is 1–10 h.

[0014] The beneficial effects of the present invention include at least the following: This invention prepares high-purity, ultrafine magnesium aluminum spinel powder. After ball milling, spray granulation, dry pressing, and cold isostatic pressing, the powder is sintered at low temperature in an atmospheric pressure and air atmosphere to prepare dense, fine-grained magnesium aluminum spinel ceramics. The ceramics have reliable strength, the process is simple and highly repeatable, which is conducive to large-scale industrialization. This invention fully solves the current problems faced by magnesium aluminum spinel ceramics and is beneficial to their practical large-scale application. Attached Figure Description

[0015] Figure 1The image shows the XRD pattern of the magnesium aluminum spinel powder prepared in Example 1. Figure 2 Here are SEM images of the magnesium aluminum spinel powder after ball milling in Example 1; Figure 3 This is a SEM image of the spray granulation process in Example 1; Figure 4 This is a cross-sectional SEM image of the ceramic green body after cold isostatic pressing in Example 1; Figure 5 This is a cross-sectional SEM image of the ceramic after sintering in Example 1. Detailed Implementation

[0016] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0017] Example: A method for preparing dense, fine-grained magnesium aluminum spinel ceramics by low-temperature sintering, comprising the following steps: S1: Mix ethanolamine, magnesium acetate tetrahydrate and water in a certain proportion to obtain mixed solution A; S2: Citric acid, aluminum isopropoxide, and water are mixed in a certain proportion to obtain mixed solution B; S3: Slowly add the mixed solution A obtained in step S1 to the solution B in step S2 to form a uniform colloid; S4: Dry the colloidal liquid obtained in step S3 to obtain a dried precursor; S5: The precursor obtained in step S4 is calcined at low temperature to obtain nano-magnesium aluminum spinel powder. S6: The magnesium aluminum spinel powder obtained in step S5 is ball-milled and spray-granulated to obtain spherical granulated powder with uniform particle size. S7: The magnesium aluminum spinel granulated powder obtained in step S6 is subjected to dry pressing and cold isostatic pressing to obtain a ceramic green body to be sintered. S8: Place the ceramic blank formed in step S7 onto an alumina sintering plate and sinter it in a muffle furnace to obtain the final magnesium aluminum spinel ceramic.

[0018] In step S1, the mass ratio of ethanolamine, magnesium acetate tetrahydrate, and water is 1:(1-20):(30-100). In step S2, the mass ratio of citric acid, aluminum isopropoxide, and water is 1:(10-60):(30-100). The mass ratio of ethanolamine in solution A to aluminum isopropoxide in solution B is 1:(10-60).

[0019] In step S1, the mixing reaction temperature is 30–100°C, and the reaction time is 1–60 h.

[0020] In step S2, the mixing reaction temperature is 30–100°C, and the reaction time is 1–60 h.

[0021] The reaction time in step S3 is 1 to 60 hours.

[0022] In step S4, the drying temperature is 30–100°C, and the drying time is 1–60 h.

[0023] In step S5, the calcination temperature is 700–1200℃ and the calcination time is 1–10 h.

[0024] In step S6, the ball milling method is planetary ball milling, the ball milling speed is 200-400 rpm, and the ball milling time is 10-30 h.

[0025] In step S7, the pressure for dry pressing is 10-50 MPa, the pressure for cold isostatic pressing is 200-300 MPa, and the pressure is held for 5 minutes.

[0026] In step S8, the sintering temperature is 1200–1400℃ and the sintering time is 1–10 h.

[0027] Example 1 S1: Dissolve 10g ethanolamine and 53.6g magnesium acetate tetrahydrate in 500g deionized water and react at 40℃ for 20h. S2: Dissolve 10g of citric acid and 205g of aluminum isopropoxide in 500g of deionized water and react at 60℃ for 20h. S3: Add the mixed solution from step S1 dropwise to the solution from step S2 and stir for 20 hours to obtain a uniform gel. S4: Dry the homogeneous precursor solution from step S3 at a temperature of 60°C for 40 hours. S5: The dried precursor from step S4 was calcined in a muffle furnace at 700℃ for 3 hours. XRD analysis of the calcined powder revealed it to be a single-phase magnesium-aluminum spinel phase. (See attached image) Figure 1 ; S6: The magnesium aluminum spinel powder obtained in step S5 was ball-milled using anhydrous ethanol as the solvent and zirconia balls as the grinding media. The ball milling speed was 270 rpm, and the milling time was 28 hours. The slurry was then filtered out, a binder was added, and spray granulation was performed to obtain spherical granulated powder with uniform particle size. The ball-milled magnesium aluminum spinel powder consisted of uniform spherical particles with a particle size of approximately 20 nm. (See...) Figure 2 After ball milling, the powder is spray-granulated into spherical particles, see... Figure 3 ; S7: The magnesium-aluminum spinel granulated powder obtained in step S6 is subjected to dry pressing and cold isostatic pressing. The dry pressing pressure is 10 MPa, and the cold isostatic pressing pressure is 200 MPa, with a holding pressure of 5 min, to obtain a ceramic green body to be sintered. The green body has a uniform microstructure and no obvious agglomeration or pores. See Figure 4 ; S8: The ceramic green body formed in step S7 is placed on an alumina sintering plate and sintered in a muffle furnace at 1300℃ for 2 hours to obtain the final magnesium-aluminate spinel ceramic. The density of the sintered ceramic sample is 3.58 g / cm³. 3 The microstructure is uniform, with an average grain size of about 200 nm, and it exhibits transgranular fracture. Figure 5 The sample, measured by indentation, had a hardness of 16.2 GPa and a fracture toughness of 3.5 MPa. 1 / 2 .

[0028] The preparation methods of Examples 2-6 are basically the same as those of Example 1, except that the ratio of solution A and solution B and the calcination temperature are changed, as detailed in Table 1 below: Table 1

[0029] Comparative examples 1-3 are as follows: Comparative Example 1 Step 1: Dry pressing and cold isostatic pressing are performed on the French Baikowski S 25 CR spinel powder. The dry pressing pressure is 10 MPa and the cold isostatic pressing pressure is 200 MPa. The pressure is held for 5 minutes to obtain the ceramic green body to be sintered. Step 2: Place the ceramic green body formed in Step 1 onto an alumina sintering plate and sinter it in a muffle furnace at 1300℃ for 2 hours to obtain the final magnesium-aluminate spinel ceramic. The density of the sintered ceramic sample is 2.5 g / cm³. 3 .

[0030] Comparative Example 2 Step 1: Same as Comparative Example 1; Step 2: Place the ceramic green body formed in Step 1 onto an alumina sintering plate and sinter it in a muffle furnace at 1500℃ for 5 hours to obtain the final magnesium-aluminate spinel ceramic. The density of the sintered ceramic sample is 3.3 g / cm³. 3 .

[0031] Comparative Example 3 Step 1: Same as Comparative Example 1; Step 2: Place the ceramic green body formed in Step 1 onto an alumina sintering plate and sinter it in a muffle furnace at 1600℃ for 5 hours to obtain the final magnesium aluminate spinel ceramic. The density of the sintered ceramic sample is 3.57 g / cm³. 3 .

[0032] The cross-sectional SEM images of the sintered ceramic and the examples show that the density of the magnesium-aluminate spinel ceramic of this application is ≥3.25 g / cm³. 3 This led to the preparation of dense, fine-grained magnesium aluminum spinel ceramics, which is beneficial for their large-scale practical application.

[0033] The above are merely embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural transformations made based on the content of the present invention specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing dense, fine-grained magnesium aluminum spinel ceramics by low-temperature sintering, characterized in that: Includes the following steps: S1: Mix ethanolamine, magnesium acetate tetrahydrate and water in a certain proportion to obtain mixed solution A; S2: Citric acid, aluminum isopropoxide, and water are mixed in a certain proportion to obtain mixed solution B; S3: Slowly add the mixed solution A obtained in step S1 to the solution B in step S2 to form a uniform colloid; S4: Dry the colloidal liquid obtained in step S3 to obtain a dried precursor; S5: The precursor obtained in step S4 is calcined at low temperature to obtain nano-magnesium aluminum spinel powder. S6: The magnesium aluminum spinel powder obtained in step S5 is ball-milled and spray-granulated to obtain spherical granulated powder with uniform particle size. S7: The magnesium aluminum spinel granulated powder obtained in step S6 is subjected to dry pressing and cold isostatic pressing to obtain a ceramic green body to be sintered. S8: Place the ceramic blank formed in step S7 onto an alumina sintering plate and sinter it in a muffle furnace to obtain the final magnesium aluminum spinel ceramic.

2. The method for preparing dense, fine-grained magnesium aluminum spinel ceramics by low-temperature sintering according to claim 1, characterized in that: In step S1, the mass ratio of ethanolamine, magnesium acetate tetrahydrate, and water is 1:(1-20):(30-100). In step S2, the mass ratio of citric acid, aluminum isopropoxide, and water is 1:(10-60):(30-100). The mass ratio of ethanolamine in solution A to aluminum isopropoxide in solution B is 1:(10-60).

3. The method for preparing dense, fine-grained magnesium aluminum spinel ceramics by low-temperature sintering according to claim 1, characterized in that: In step S1, the mixing reaction temperature is 30–100°C, and the reaction time is 1–60 h.

4. The method for preparing dense, fine-grained magnesium aluminum spinel ceramics by low-temperature sintering according to claim 1, characterized in that: In step S2, the mixing reaction temperature is 30–100°C, and the reaction time is 1–60 h.

5. The method for preparing dense, fine-grained magnesium aluminum spinel ceramics by low-temperature sintering according to claim 1, characterized in that: The reaction time in step S3 is 1 to 60 hours.

6. The method for preparing dense, fine-grained magnesium aluminum spinel ceramics by low-temperature sintering according to claim 1, characterized in that: In step S4, the drying temperature is 30–100°C, and the drying time is 1–60 h.

7. The method for preparing dense, fine-grained magnesium aluminum spinel ceramics by low-temperature sintering according to claim 1, characterized in that: In step S5, the calcination temperature is 700–1200℃ and the calcination time is 1–10 h.

8. The method for preparing dense, fine-grained magnesium aluminum spinel ceramics by low-temperature sintering according to claim 1, characterized in that: In step S6, the ball milling method is planetary ball milling, the ball milling speed is 200-400 rpm, and the ball milling time is 10-30 h.

9. The method for preparing dense, fine-grained magnesium aluminum spinel ceramics by low-temperature sintering according to claim 1, characterized in that: In step S7, the pressure for dry pressing is 10-50 MPa, the pressure for cold isostatic pressing is 200-300 MPa, and the pressure is held for 5 minutes.

10. The method for preparing dense, fine-grained magnesium aluminum spinel ceramics by low-temperature sintering according to claim 1, characterized in that: In step S8, the sintering temperature is 1200–1400℃ and the sintering time is 1–10 h.

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